The invention relates generally to the field of precious metal decorations for ceramics and in particular to a decorative composition producing the appearance of gold after firing, but which actually contains no metallic gold.
Decorative compositions for ceramics to achieve a gold appearance have heretofore contained substantial quantities of metallic gold, often of the order of 10-15 weight percent with the balance being fluxing agents and vehicle. Such prior art decorations are disclosed in such patents as U.S. Pat. Nos. 2,994,614 and 3,092,504 which disclose and claim specific gold compounds and compositions which were found useful for decorations having a gold appearance. The maximum gold content is determined primarily by the cost of the gold and the fact that increasing the gold content beyond certain levels does not further improve the appearance. The minimum gold content of such decorations is determined primarily by the poorer adherence and durability of low gold content films and the deterioration in their appearance. It will be appreciated that until recent years gold, although a precious metal, was less expensive than some of the other precious metals. As the price of gold has risen, it has become of interest to reduce the quantity of gold used in decorations since at 4 to 5 times the previous cost the use of gold in decorating compositions becomes prohibitive, except for the most expensive articles.
Palladium has also been used in decorative compositions. In some compositions, it produced a white metal appearance when used in combination with gold, and simulates the heretofore more expensive platinum compositions. In other applications, it has been used to produce a brown color. Thus, in the prior art, palladium has been used both to produce a white color in combination with large amounts of gold, and to produce a brown color when no gold is present. Examples may be found in U.S. Pat. No. 3,216,834, the disclosure of which is incorporated by reference herein, which is principally directed to a new compound of palladium for use in decorative applications. In one example of the patent, a composition containing 1.5 percent palladium, 3 percent silver, and much smaller amounts of rhodium and chromium is shown to produce a chocolate brown color useful for decoration. In other examples, bright palladium decorating compositions are shown to contain large quantities of gold and smaller amounts of palladium. Other patents disclosing palladium compounds useful for decorative applications include U.S. Pat. Nos. 3,718,488 and 3,770,785. The disclosure of U.S. Pat. No. 3,216,834, which is assigned to the assignee of this application, also sets forth a number of the essential oils and hydrocarbon solvents conventionally used in the art.
Palladium has also been used with silver in a film which has the ability to separate gaseous mixtures by hydrogen diffusion through the film. U.S. Pat. No. 3,413,777 discloses such a film which contains an alloy of 5-40 weight percent silver and the remainder palladium, the alloy being mixed with a glaze in the method of forming the desired film.
Silver, when used alone, produces a film having an amber appearance. What has been desired since the cost of gold has increased many-fold is a decoration for ceramics which, while giving the appearance of gold after firing, does not contain substantial quantities of that metal, in order that the cost may be kept at reasonable levels. This objective has been accomplished by the composition and the method of the present invention, in which no metallic gold is used.